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serialize

(PHP 4, PHP 5)

serializeGenera una representación apta para el almacenamiento de un valor

Descripción

string serialize ( mixed $value )

Genera una representación almacenable de un valor.

Esto es útil para el almacenamiento de valores en PHP sin perder su tipo y estructura.

Para recuperar el valor PHP a partir de la cadena seriada, utilice unserialize().

Parámetros

value

El valor a ser serializado. serialize() maneja todos los tipos, excepto el tipo resource. Puede incluso usar serialize() sobre arrays que contienen referencias a ellos mismos. Las referencias circulares encontradas en el array/objeto que procede a serializar también serán almacenadas. Cualquier otra referencia se perderá.

Cuando se trata de objetos, PHP intentará llamar a la función miembro __sleep() antes de la serialización. Esto permite que el objeto efectúe limpiezas de último minuto, etc. antes de ser serializado. Del mismo modo, cuando el objeto es recuperado usando unserialize(), la función miembro __wakeup() es llamada.

Nota:

Los miembros privados del objeto tienen el nombre de la clase al comienzo de su nombre; los miembros protegidos tienen un '*' al comienzo de su nombre. estos valores antepuestos tienen bytes nulos a ambos lados.

Valores devueltos

Devuelve una cadena que contiene una representación de flujo de bytes del value que puede ser almacenada en cualquier parte.

Observe que esto es una cadena binaria que puede incluir bytes nulos, y necesita ser almacenada y manipulada como tal. Por ejemplo, la salida de serialize() debe ser generalmente almacenada en un campo de tipo BLOB en la base de datos, en vez de en campos de tipo CHAR o TEXT.

Ejemplos

Ejemplo #1 Ejemplo serialize()

<?php
// $datos_sesion contiene un array multi-dimensional con
// información del usuario actual. Usamos serialize() para
// almacenarla en una base de datos al final de la petición.

$con  odbc_connect("bd_web""php""gallina");
$sent odbc_prepare($con,
      
"UPDATE sesiones SET datos = ? WHERE id = ?");
$datos_sql = array (serialize($datos_sesion), $_SERVER['PHP_AUTH_USER']);

if (!
odbc_execute($sent, &$datos_sql)) {
    
$sent odbc_prepare($con,
     
"INSERT INTO sesiones (id, datos) VALUES(?, ?)");
    if (!
odbc_execute($sent, &$datos_sql)) {
        
/* Algo ha fallado.. */
    
}
}
?>

Historial de cambios

Versión Descripción
4.0.7 El proceso de serialización de objetos fue corregido.

Notas

Nota:

Tenga en cuenta que muchos objetos integrados de PHP no se pueden serializar. Sin embargo, aquellos con esta habilidad o implementan la interfaz Serializable o los métodos mágicos __sleep() y __wakeup(). Si una clase interna no cumple cualquiera de esos requisitos, estas seguramente no puedan ser serializadas.

Hay algunas excepciones históricas a la regla anterior, donde algunos objetos internos podrían ser serializados sin implementar la interfaz o la exposición de los métodos. En particular, la clase ArrayObject anterior a PHP 5.2.0.

Advertencia

Cuando serialize() serializa los objetos, la barra inicial no está incluido en el nombre de clase de las clases de espacios de nombres para una máxima compatibilidad.

Ver también

add a note add a note

User Contributed Notes 25 notes

up
52
egingell at sisna dot com
8 years ago
<?
/*
Anatomy of a serialize()'ed value:

String
s:size:value;

Integer
i:value;

Boolean
b:value; (does not store "true" or "false", does store '1' or '0')

Null
N;

Array
a:size:{key definition;value definition;(repeated per element)}

Object
O:strlen(object name):object name:object size:{s:strlen(property name):property name:property definition;(repeated per property)}

String values are always in double quotes
Array keys are always integers or strings
    "null => 'value'" equates to 's:0:"";s:5:"value";',
    "true => 'value'" equates to 'i:1;s:5:"value";',
    "false => 'value'" equates to 'i:0;s:5:"value";',
    "array(whatever the contents) => 'value'" equates to an "illegal offset type" warning because you can't use an
    array as a key; however, if you use a variable containing an array as a key, it will equate to 's:5:"Array";s:5:"value";',
     and
    attempting to use an object as a key will result in the same behavior as using an array will.
*/
?>
up
18
nh at ngin dot de
1 year ago
Serializing floating point numbers leads to weird precision offset errors:

<?php

echo round(96.670000000000002, 2);
// 96.67

echo serialize(round(96.670000000000002, 2));
// d:96.670000000000002;

echo serialize(96.67);
// d:96.670000000000002;

?>

Not only is this wrong, but it adds a lot of unnecessary bulk to serialized data. Probably better to use json_encode() instead (which apparently is faster than serialize(), anyway).
up
8
MC_Gurk at gmx dot net
8 years ago
If you are going to serialie an object which contains references to other objects you want to serialize some time later, these references will be lost when the object is unserialized.
The references can only be kept if all of your objects are serialized at once.
That means:

$a = new ClassA();
$b = new ClassB($a); //$b containes a reference to $a;

$s1=serialize($a);
$s2=serialize($b);

$a=unserialize($s1);
$b=unserialize($s2);

now b references to an object of ClassA which is not $a. $a is another object of Class A.

use this:
$buf[0]=$a;
$buf[1]=$b;
$s=serialize($buf);
$buf=unserialize($s);
$a=$buf[0];
$b=$buf[1];

all references are intact.
up
6
frost at easycast dot ru
10 months ago
Closures cannot be serialized:
<?php
$func
= function () {echo 'hello!';};
$func(); // prints "hello!"

$result = serialize($func);  // Fatal error: Uncaught exception 'Exception' with message 'Serialization of 'Closure' is not allowed'
?>
up
8
wiart at yahoo dot com
9 years ago
Warning: on 64 bits machines,  if you use a long string only composed of numbers as a key in an array and serialize/unserialize it, you can run into problems:

an example code:
$arr["20041001103319"] = 'test';
var_dump( $arr);
$arr_in_str = serialize($arr);
print "Now result is: $arr_in_str<BR />";
$final_arr = unserialize($arr_in_str);
print "The final unserialized array:<BR />";
var_dump($final_arr);

The result:
array(1) { [20041001103319]=>  string(4) "test" }
Now result is: a:1:{i:20041001103319;s:4:"test";}
The final unserialized array:
array(1) { [683700183]=> string(4) "test" }

As you can see, the original array :
$arr["20041001103319"] = "test"

after serialize/unserialize is:
$arr[683700183] = "test"

As you can see,  the key has changed ...

Apparently a problem of implicit casting + integer overflow (I posted a PHP bug report: http://bugs.php.net/bug.php?id=31117)

I tested with the latest 4.3.10 compiled on my laptop (32 bits, Mandrake 9.1) --> no such problem. But compiled on AMD 64 bits (Red Hat Taroon), the problem is present.

Hope this will help some of you to not loose almost a whole day of debugging ;-)
up
10
Anonymous
2 years ago
Please! please! please! DO NOT serialize data and place it into your database. Serialize can be used that way, but that's missing the point of a relational database and the datatypes inherent in your database engine. Doing this makes data in your database non-portable, difficult to read, and can complicate queries. If you want your application to be portable to other languages, like let's say you find that you want to use Java for some portion of your app that it makes sense to use Java in, serialization will become a pain in the buttocks. You should always be able to query and modify data in the database without using a third party intermediary tool to manipulate data to be inserted.

I've encountered this too many times in my career, it makes for difficult to maintain code, code with portability issues, and data that is it more difficult to migrate to other RDMS systems, new schema, etc. It also has the added disadvantage of making it messy to search your database based on one of the fields that you've serialized.

That's not to say serialize() is useless. It's not... A good place to use it may be a cache file that contains the result of a data intensive operation, for instance. There are tons of others... Just don't abuse serialize because the next guy who comes along will have a maintenance or migration nightmare.
up
2
Alexander Podgorny
8 years ago
Here is an example of a base class to implement object persistence using serialize and unserialize:

<?php
class Persistent
{
    var
$filename;
       
   
/**********************/
   
function Persistent($filename)
    {
       
$this->filename = $filename;
        if(!
file_exists($this->filename)) $this->save();
    }
   
/**********************/
   
function save()
    {
        if(
$f = @fopen($this->filename,"w"))
        {
            if(@
fwrite($f,serialize(get_object_vars($this))))
            {
                @
fclose($f);
            }
            else die(
"Could not write to file ".$this->filename." at Persistant::save");
        }
        else die(
"Could not open file ".$this->filename." for writing, at Persistant::save");
       
    }
   
/**********************/
   
function open()
    {
       
$vars = unserialize(file_get_contents($this->filename));
        foreach(
$vars as $key=>$val)
        {           
            eval(
"$"."this->$key = $"."vars['"."$key'];");
        }
    }
   
/**********************/
}

?>

When an object is extended from this one it can be easily saved and re-opened using it's own methods as follows:

<?

class foo extends Persistent
{
   var $counter;
   function inc()
   {
       $this->counter++;
   }
}

$fooObj = new $foo;
$foo->open();
print $foo->counter; // displays incrementing integer as page reloads
$foo->inc();
$foo->save();

?>
up
2
Andrew B
1 year ago
When you serialize an array the internal pointer will not be preserved. Apparently this is the expected behavior but was a bit of a gotcha moment for me. Copy and paste example below.

<?php
//Internal Pointer will be 2 once variables have been assigned.
$array = array();
$array[] = 1;
$array[] = 2;
$array[] = 3;

//Unset variables. Internal pointer will still be at 2.    
unset($array[0]);
unset(
$array[1]);
unset(
$array[2]);

//Serialize
$serializeArray = serialize($array);

//Unserialize
$array = unserialize($serializeArray);

//Add a new element to the array
//If the internal pointer was preserved, the new array key should be 3.
//Instead the internal pointer has been reset, and the new array key is 0.
$array[] = 4;

//Expected Key - 3
//Actual Key - 0
echo "<pre>" , print_r($array, 1) , "</pre>";
?>
up
1
Jeex
6 years ago
It may be worth noting that, depending on the size of the object you are serializing, the serialize function can take up a lot of memory.

If your script isn't working as expected, your serialize call may have pushed the memory usage over the limit set by memory_limit in php.ini.

More info on memory limits here: http://www.php.net/manual/en/ini.core.php
up
1
Ates Goral
8 years ago
Corrections/clarifications to  "Anatomy of a serialize()'ed value":

All strings appear inside quotes. This applies to string values, object class names and array key names. For example:

s:3:"foo"
O:7:"MyClass":1:{...
a:2:{s:3:"bar";i:42;...

Object property names and values are delimited by semi-colons, not colons. For example:

O:7:"MyClass":2:{s:3:"foo";i:10;s:3:"bar";i:20}

Double/float values are represented as:

d:0.23241446
up
1
MarkRoedel at letu dot edu
14 years ago
A call to serialize() appears to mess with the array's internal pointer.  If you're going to be walking through your array after serializing it, you'll want to make a call to reset() first.
up
1
pgl at yoyo dot org
3 years ago
Another suggestion for coping with binary data in serialize()d variables is just to base64_encode() those fields before serializing. It will increase the size of the variable, but not by too much.
up
1
tuxedobob
1 month ago
When using serialize() to convert, say, an array to a string to pass via HTML forms, you will likely run into issues with quoting. This is because serialize() puts values in double quotes. The simplest solution is to quote your HTML form value with single quotes rather than double quotes. (This *is* allowed, according to W3C specs.)

So, instead of:

<?php
$arr
= serialize($some_array);
?>
<input type="hidden" name="array" value="$arr" />

you would want to use:

<?php
$arr
= serialize($some_array);
?>
<input type="hidden" name="array" value='$arr' />
up
0
stephen dot adamson at smius dot com
8 years ago
If you are serializing an object to store it in the database, using __sleep() can save you some space. The following code will not store empty (null) variables in the serialized string. For my purposes this saved a lot of space, since some of the member variables would not be given values.

function __sleep()
{
    $allVars = get_object_vars($this);
    $toReturn = array();
    foreach(array_keys($allVars) as $name)
    {
        if (isset($this->$name))
        {
            $toReturn[] = $name;
        }
    }
    return $toReturn;
}
up
0
paul at moveNOtoSPAMiceland DOT com
9 years ago
I was trying to submit a serialized array through a hidden form field using POST and was having a lot of trouble with the quotes. I couldn't figure out a way to escape the quotes in the string so that they'd show up right inside the form, so only the characters up to the first set of quotes were being sent.

My solution was to base64_encode() the string, put that in the hidden form field, and send that through the POST method. Then I decoded it (using base64_decode()) on the other end. This seemed to solve the problem.
up
0
hfuecks at phppatterns dot com
10 years ago
Regarding serializing PHP data types to Javascript, following Ivans note below, theres an example at http://www.tekool.net/php/js_serializer/.

The basic serialization looks good although, in its current form, it works on the basis of generating Javascript source which a browser executes as a page loads. Using Javascripts eval() the same can be done with strings containing Javascript if youre working with something like XMLHTTPRequest
up
0
pli9 at itsa dot ucsf dot edu
11 years ago
I have also written some code for importing serialized PHP data into PERL and then writing it back into PHP.  I think the similar library posted above is actually more robust for a few select cases, but mine is more compact and a little easier to follow.  I'd really like comments if anyone finds this useful or has improvements.  Please credit me if you use my code.

http://www.hcs.harvard.edu/~pli/code/serialPHP.pm
up
-1
travis at travishegner dot com
4 years ago
If serializing objects to be stored into a postgresql database, the 'null byte' injected for private and protected members throws a wrench into the system. Even pg_escape_bytea() on the value, and storing the value as a binary type fails under certain circumstances.

For a dirty work around:
<?php

$serialized_object
= serialize($my_object);
$safe_object = str_replace("\0", "~~NULL_BYTE~~", $serialized_object);

?>

this allows you to store the object in a readable text format as well. When reading the data back:

<?php

$serialized_object
= str_replace("~~NULL_BYTE~~", "\0", $safe_object);
$my_object = unserialize($serialized_object);

?>

The only gotcha's with this method is if your object member names or values may somehow contain the odd "~~NULL_BYTE~~" string. If that is the case, then str_replace() to a string that you are guaranteed not to have any where else in the string that serialize() returns.
Also remember to define the class before calling unserialize().

If you are storing session data into a postgresql database, then this workaround is an absolute must, because the $data passed to the session's write function is already serialized.

Thanks,
Travis Hegner
up
-1
barbuj at NOSPAM dot yahoo dot com
6 years ago
In my specific situation, I wanted to be able to pass some data from page to page, but without relying on a session variable. The answer I came up with was to serialize() the object in question, pass it on to the next page as a hidden form field, then unserialize() it. When ALL class variables are public, this worked fine. However, if there was at least one private/protected variable, the code no longer worked as expected ("Fatal error: Call to a member function display() on a non-object in page2.php on line 4")

As others have already mentioned, private/protected class variables will not behave nicely (private variables are prefixed by class_name + &#65533;, while protected variables are only prefixed by &#65533; - when looking at the page source using Firefox). Internet Explorer does NOT display the extra character between the class name and variable name, but the code still doesn't work as one would expect.

Suppose you have a simple class:

testclass.php
=============
<?php
class TestClass {
  var
$i = 1;

  function
display() {
    echo
"i=" . $this->i;
  }
?>

page1.php
=========
<?php
 
require_once 'testclass.php';
 
$tc = new TestClass;
 
$tc->display();
?>
<form method = "post" action = "page2.php">
<input type = "hidden" name = "str" value = "<?php echo htmlspecialchars( serialize( $tc ) ); ?>">
<input type = "submit">
</form>

page2.php
=========
<?php
 
require_once 'testclass.php';
 
$tc = unserialize( stripslashes( htmlspecialchars_decode( $_POST["str"] ) ) );
 
$tc->display();
?>

The fix, suggested by evulish on #php/irc.dal.net, is to replace htmlspecialchars()/htmlspecialchars_decode() by base64_encode()/base64_decode. The code becomes:

page1.php
=========
<input type = "hidden" name = "str" value = "<?php echo base64_encode( serialize( $tc ) ); ?>">

page2.php
=========
<?php
  $tc
= unserialize( base64_decode( $_POST["str"] ) );
?>

Hope this will help someone...
up
-1
Anonymous
4 years ago
you should really use mysql_real_escape_string() for escaping (serialized) strings that got thrown into a query (visit php.net/mysql_real_escape_string for further information)
up
-1
allan666 at gmail.com
1 year ago
Oddly, if you serialize a class that was previously unserialized, the class of the variable changes to string... Example:

$R = unserialize($serialized_object);
$R->method(); // this is ok
$str = serialize($R);
echo(get_class($R));

this will output "string"!!!!! whereas if the first line was

$R = new my_class();

it would output "my_class"!

I don't know if that is a bug, but the manual is not clear about that! (somehow $R in serialize($R) is being passed by reference, since it changes class).
up
-2
friday13 at ig dot com dot br
7 years ago
I have problem to use serialize function with hidden form field and the resolution was use htmlentities.

Ex.:

<?

$lista = array( 'pera', 'maça', 'laranja' );

print "< input type='hidden' name='teste' value='htmlentities( serialize( $lista ) )'" >";

?>
up
-2
donotmail at me dot com
4 years ago
NOTE: php's serialize does not properly serialize arrays with which a slice of the array is a reference to the array itself, observe:

<?php
$a
= array();
$a[0] = "blah";
$a[1] =& $a;

$a[1][0] = "pleh"; // $a[0] === "pleh"

$b = unserialize(serialize($a));

// $b[0] == "pleh", $b[1][0] == "pleh"

$b[1][0] = "blah";
?>

now $b[1][0] == "blah", but $b[0] == "pleh"
after serializing and unserializing, slice 1 is no longer a reference to the array itself... I have found no way around this problem... even manually modifying the serialized string from
'a:2:{i:0;s:4:"pleh";i:1;a:2:{i:0;s:4:"pleh";i:1;R:3;}}'
to
'a:2:{i:0;s:4:"pleh";i:1;R:1;}'

to force the second slice to be a reference to the first element of the serialization (the array itself), it seemed to work at first glance, but then unreferences it when you alter it again, observe:

<?php
    $testser
= 'a:2:{i:0;s:4:"pleh";i:1;R:1;}';

   
$tmp = unserialize($testser);

   
print_r($tmp);

    print
"\n-----------------------\n";

   
$tmp[1][0] = "blah";

   
print_r($tmp);

?>

outputs:
Array
(
    [0] => pleh
    [1] => Array
*RECURSION*
)

-----------------------
Array
(
    [0] => pleh
    [1] => Array
        (
            [0] => blah
            [1] => Array
                (
                    [0] => pleh
                    [1] => Array
*RECURSION*
                )

        )

)
up
-2
Alessandro Segala
5 years ago
I needed to serialize an array to store it inside a database.
I was looking for a fast, simple way to do serialization, and I came out with 2 options: serialize() or json_encode().

I ran some benchmarks to see which is the faster, and, surprisingly, I found that serialize() is always between 46% and 96% SLOWER than json_encode().
So, if you don't need to serialize objects and have the json extension available, consider using it instead of serialize().
up
-1
Nanhe Kumar
7 months ago
Note : You cannot save the state of a static variable by serializing.
<?php
/*
* student.class.php
*/
class Student {

    public
$name;
    private
$roll;
    protected
$age;
    static
$class;

    public function
__construct() {
       
$this->name = "Nanhe Kumar";
       
$this->roll = 1;
       
$this->age = 16;
       
Student::$class = "10+2";
    }

}
?>
<?php
/**
* serialize.php
*/
include_once("student.class.php");

//Serialize
$so = new Student();
$serialized = serialize($so);
file_put_contents("test.txt", $serialized);
echo
$serialized; //O:7:"Student":3:{s:4:"name";s:11:"Nanhe Kumar";s:13:"Studentroll";i:1;s:6:"*age";i:16;}
?>
<?php
/**
* unserialize.php
*/
include_once("student.class.php");
$content = file_get_contents("test.txt");
$unserialized = unserialize($content);
print_r($unserialized);//Student Object ( [name] => Nanhe Kumar [roll:Student:private] => 1 [age:protected] => 16 )
?>
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